Traditional paint spray systems, of the type employed in car manufacturing for example, usually consist of several separate paint lines, each providing a different coloured paint to a spray booth for distribution to a number of user points (e.g. spray applicators). In general, only one colour is sprayed or in use at any one time, so only one line is actively employed whilst the rest remain ready for use.
When a system is not in use because the paint is not being sprayed, it is usual to maintain the spraying pressure and paint velocity in the paint line, by pumping paint from a paint tank around a circuit and back to the tank. This is done for two reasons: firstly, because the liquid paint must be kept moving, otherwise pigmentation may start to settle out in the paint lines; secondly, because the lines must be primed to the required pressure before spraying commences. However, maintaining the lines at pressure is wasteful of energy.
To ensure that the paint is at the required pressure for spraying, a Back Pressure Regulator (BPR) is used in combination with the paint pump to regulate and maintain the required fluid pressure and flow at the spray booth. In conventional systems, the BPR is adjusted manually and uses a coil spring acting on a diaphragm to vary the width of a flow passage. This helps to maintain the paint pressure upstream of the BPR by controlling the fluid flow rate returning to the paint tank. Also, in many systems (such as those employing certain types of turbine or lobe pumps) the pump will be set to operate at a fixed pressure and flow rate and the BPR used to maintain the required system pressure. In this type of system, the BPR controls system pressure by adjusting flow rate to compensate for variations in the amount of fluid used at the spray booth. Thus, each line is usually operated in the condition required for spraying, whether the paint is being used or merely circulated. This is extremely inefficient and results a large waste of energy. For example, a system operating 24 hours a day may only be required to spray each individual colour, for, say, 1 hour a day. Each pump would be operated at the pressure and flow rate required to meet the system requirement for 24 hours a day even though the paint is not required to operate at the full system pressure and flow rate for 23 hours of the day.
In addition, a pump that is required to provide a higher flow rate and pressure for a longer period of time will suffer a higher rate of wear, requiring maintenance in a much shorter period of time than one that is used more sparingly.
It is an object of the present invention to provide a paint circulation system, which alleviates the aforementioned problems.